Method, computer program and control and/or regulating appliance for operating an internal combustion engine, and corresponding internal combustion engine

ABSTRACT

An internal combustion engine ( 10 ), especially of a motor vehicle, is operated with a method wherein the fuel is injected directly into a combustion chamber ( 12 ) of the internal combustion engine ( 10 ) with at least one injection ( 36 ) per work cycle. In order to reduce the fuel consumption and to improve the emission performance of the internal combustion engine ( 10 ), it is suggested that a fuel injection ( 36 ) includes a plurality of short injection pulses ( 32 ) spaced in time from each other.

This application is the U.S. national stage of international applicationNo. PCT/DE 02/00394, filed Feb. 4, 2002, designating the United States.

FIELD OF THE INVENTION

The present invention relates to a method for operating an internalcombustion engine, especially of a motor vehicle wherein the fuel isinjected directly into a combustion chamber of the engine with at leastone injection per work cycle.

BACKGROUND OF THE INVENTION

A method of this kind is known from the marketplace. The method is alsoknown as gasoline direct injection. In this method, the fuel is injectedinto the combustion chamber of the engine at very high pressure viainjection valves mounted directly at the combustion chamber. The engineoperates cyclically. In a four-stroke internal combustion engine, a workcycle includes, for example, four work strokes.

In the known method, it was, however, determined that the total injectedfuel does not always combust optimally. In some operating states of theengine, this leads to a fuel use which is still not economicallyoptimal. Furthermore, an incomplete combustion of the injected fuelleads to hydrocarbon emissions or soot emissions. It was determined thatthis problem occurs more intensely in the cold state of the engine.

SUMMARY OF THE INVENTION

The present invention therefore has the task to improve a method of thekind mentioned initially herein so that the fuel use is still furtheroptimized and the emissions are simultaneously reduced.

The task is solved with a method of the kind described above in that afuel injection includes a plurality of short injection pulses spaced intime from each other.

The method of the invention is based on the following idea. The fuel isinjected very early and in some circumstances already at the start ofthe downward movement of the piston in the induction phase in order toachieve homogenization, that is, a mixture of the injected fuel with theair in the combustion chamber as uniform as possible. In this phase, thepressure in the combustion chamber is relatively low and amountstypically to less than 1 bar. It was determined that, for longer openingtimes of the injection valve at so low a pressure in the combustionchamber, the fuel from the injection valve impinges against the wall ofthe combustion chamber lying opposite to the injection valve and adheresto this wall as a layer. However, a layer on the wall of the combustionchamber comprising fuel can be vaporized only with difficulty andtherefore leads to a non-optimal mixture in the combustion chamber.

The duration of an individual short injection pulse of the plurality ofinjection pulses of a single fuel injection is considerably shorter thanthe total duration of the individual fuel injection. A short injectionpulse is understood to mean, according to the invention, a pulse whereinonly a small part of the fuel quantity, which is to be introduced withthe individual injection into the combustion chamber of the engine, isactually injected. Such an injection pulse therefore distinguishes fromthe individual injections of double or triple injections known today.

In this way, the depth of penetration of the fuel drops in such aninjection pulse. In this way, it is prevented that the fuel, which isinjected into the combustion chamber with an injection pulse, impingesagainst the wall lying opposite to the injection valve and leads to thewall application mentioned initially herein. The shorter the duration ofthe injection pulse, the more it is ensured that the fuel injected inthis way mixes with the air disposed in the combustion chamber and doesnot deposit on the wall of the combustion chamber. In the method of theinvention, no continuous injection therefore takes place, rather, apulsed injection takes place which is also characterized as a choppedinjection.

In the method of the invention, the fuel injected into the combustionchamber essentially mixes completely with the air disposed in thecombustion chamber. For this reason, the fuel is optimally combustedwhich reduces the specific fuel consumption and improves the emissionperformance. The deposit of the injected fuel on the wall of thecombustion chamber for a cold combustion chamber wall is especiallysignificant and this deposit occurs less or not at all in the method ofthe invention. For this reason, the cold start method of the internalcombustion engine is improved with the method of the invention in aspecial way.

In a first embodiment, the fuel quantity, which gets into the combustionchamber with an injection, is adjusted at least also by the duration ofthe individual injection pulses. For controlling the power of theinternal combustion engine, it has to be possible to adjust the totalfuel quantity which is injected per work stroke into the combustionchamber. For this, the adjustment of the duration of the individualinjection pulse offers a simple possibility. However, attention must bepaid to the situation that the duration of a single injection pulsenever reaches that duration for which the critical penetration depth isexceeded. Under critical penetration depth, that penetration depth isunderstood for which the injected fuel impinges on the wall of thecombustion chamber lying opposite to the injection valve.

It is especially preferred to adjust the power of the internalcombustion engine in that the fuel quantity, which reaches thecombustion chamber with an injection, is adjusted at least also by thenumber of the individual injection pulses.

The method of the invention is realized in the simplest way in that theinjection pulses are uniformly distributed over the entire duration ofan injection. The method of the invention is likewise simple when theduration of the injection pulses does not change over the total durationof an injection. If the injection takes place during the induction phaseof the piston, each component quantity of fuel, which is injected by aninjection pulse, lands in a new inducted air volume which leads toadvantages in the distribution of the fuel in the air in the combustionchamber.

It is, however, also possible that the time-dependent spacing betweentwo injection pulses changes over the duration of an injection. In thisway, the fact can be taken into account that the piston speed during theinduction phase is not constant and therefore the air volumes, which areinducted per unit of time, also do not have the same magnitude. Thismeans, in turn, that the fuel distribution in the air in the combustionchamber can be optimized.

It is especially preferred when the duration of the injection pulsechanges over the total duration of an injection, preferably increases.This variation of the method of the invention is especially advantageouswhen the injection takes place not only during the induction phase butalso during the compression phase of the internal combustion engine. Thepressure in the combustion chamber increases during the compressionphase of the internal combustion engine. For this reason, a moisteningof the wall can be reliably avoided with the larger injection quantitypresent with a longer injection pulse.

In an especially preferred embodiment of the method of the invention, itis provided that, at the end of an injection, an individual injectionpulse takes place which takes longer than the previous injection pulsesof the injection. With such an injection strategy, a residual quantitycan still be injected, for example, into a homogeneous lean mixture inthe combustion chamber for a piston which has risen far (that is, towardthe end of the compression phase of the engine). The residual quantitytogether with the homogeneous lean charge (which previously wasintroduced with a plurality of short injection pulses), generatesapproximately stoichiometry within the occurring mixture cloud(stratification from stoichiometric mixture cloud and homogeneous leanenvironment). This method has the advantage that extremely leanhomogeneous basic mixtures can be completely combusted because anessential part of the combustion volume was previously combustedstoichiometrically and, in this way, the homogeneous lean environmentwas heated and compressed.

In a further embodiment, approximately 5 mm³ fuel is injected perinjection pulse and/or an injection pulse has a duration of not longerthan approximately 0.5 ms. With these values, an impinging of theinjected fuel against the wall of the combustion chamber lying oppositethe injection valve is reliably prevented under normal operatingconditions.

Finally, it is noted that several fuel injections take place per workcycle of which at least one, in turn, comprises several injectionpulses. For example, it is possible to carry out an injection in theinduction phase and another injection during the compression phase ofthe internal combustion engine. Such a procedure has advantages withrespect to the knocking sensitivity of the internal combustion engine.

The present invention relates also to a computer program which issuitable for carrying out the above method when it is executed on acomputer. Here, it is especially preferred when the computer program isstored on a memory, especially on a flash memory.

Furthermore, the present invention relates to a control apparatus (openloop and/or closed loop) for operating an internal combustion engineespecially of a motor vehicle wherein the fuel is injected directly intothe combustion chamber of the engine. In order to optimize the operationof the engine with respect to the consumption of fuel and the emissionperformance, it is suggested in accordance with the invention that thecontrol apparatus (open loop and/or closed loop) is suitable forcontrolling (open loop and/or closed loop) the above method.

It is especially preferred when the control apparatus (open loop and/orclosed loop) is provided with a computer program of the above-mentionedtype.

The present invention further relates to an internal combustion enginehaving at least one combustion chamber and a device which injects thefuel directly into the combustion chamber. In order to improve theoperational performance of this engine, especially the fuel consumption,the emission performance as well as the cold start performance, it issuggested in accordance with the invention that the engine be providedwith a control apparatus (open loop and/or closed loop) of theabove-mentioned type.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described with reference to the drawingswherein:

FIG. 1 is a principle schematic of an internal combustion engine havinggasoline direct injection;

FIG. 2 is a diagram of a first embodiment of a method for operating theinternal combustion engine of FIG. 1 wherein the injected fuel quantityis shown as a function of time;

FIG. 3 is a diagram similar to FIG. 2 of a second embodiment of a methodfor operating the internal combustion engine of FIG. 1;

FIG. 4 is a diagram similar to FIG. 2 of a third embodiment of a methodfor operating the internal combustion engine of FIG. 1;

FIG. 5 is a diagram similar to FIG. 2 of a fourth embodiment of a methodfor operating the internal combustion engine of FIG. 1;

FIG. 6 is a diagram similar to FIG. 2 of a fifth embodiment of a methodfor operating the internal combustion engine of FIG. 1; and,

FIG. 7 is a diagram similar to FIG. 2 of a sixth embodiment of a methodfor operating the internal combustion engine of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

In FIG. 1, an internal combustion engine is identified by referencenumeral 10. Typically, the engine is operated in accordance with thefour-stroke principle and a work cycle therefore includes four strokes.Such an engine is, for example, used in motor vehicles. The engineincludes a combustion chamber 12 to which air is supplied via an intakemanifold 14. Fuel is injected into the combustion chamber 12 via a highpressure injection valve 16. This injection valve is fed from a fuelcollection line 18 which is also characterized as a “rail” and in whichthe fuel is made available under very high pressure. The ignition of theair/fuel mixture, which is formed in the combustion chamber 12, takesplace via an ignition device 20, preferably, a spark plug. A piston 22is moved by the expansion of the combusting air/fuel mixture. Theoperating state of the internal combustion engine 10, especially theposition of the piston 22, is detected by a sensor 24. The hotcombustion exhaust gases are conducted away via an exhaust-gas pipe 26.

The internal combustion engine 10 includes a control apparatus (openloop and/or closed loop) 28 to which the power commands of a user areimparted via an accelerator pedal 30. Furthermore, the control apparatus(open loop and/or closed loop) 28 receives signals from the sensor 24.At the output end, the apparatus 28 is, inter alia, connected to theinjection valve 16 and the ignition device 20.

The fuel is generally injected very early, that is, already at the startof the downward movement of the piston 22 in the induction phase of theinternal combustion engine 10 in order to obtain a homogenization, thatis, a mixing of the fuel, which is injected into the combustion chamber12 by the injection valve 16, with the air inducted through the intakemanifold 14 as uniformly as possible. The relevant angle of thecrankshaft (not shown) of the internal combustion engine 10 is detectedby the sensor 24 and a corresponding signal is transmitted to thecontrol apparatus (open loop and/or closed loop) 28.

A relatively low pressure (in general, at most approximately 1 bar) ispresent in the combustion chamber 12 during this phase. For this reason,the danger is present that the fuel, which is injected by the injectionvalve 16 under high pressure into the combustion chamber 12, impingesagainst the wall (not shown) of the combustion chamber 12, which liesopposite to the injection valve 16, or impinges on the upper side of thepiston 22 and adheres there. A fuel layer on the wall or on the piston22 can be vaporized only with difficulty and does not participate or atleast does not participate in the desired manner in the combustion inthe combustion chamber 12 which increases the fuel consumption anddeteriorates the emission performance. The problem of the deposit of thefuel on a wall of the combustion chamber 12 is especially significantwhen the wall of the combustion chamber 12 is cold. In this case, thecold-start performance of the internal combustion engine 10 is thereforeaffected.

The injection valve 16 is driven by the control apparatus (open loopand/or closed loop) 28 so that it opens and closes pulse-like in orderto avoid that such a deposit of fuel occurs on a wall of the combustionchamber 12. The opening time of the injection valve 16 does not exceed0.5 ms. The fuel quantity which reaches the combustion chamber 12 duringan injection pulse (that is, during an uninterrupted opening time of theinjection valve 16 ) should, in the normal case, not exceedapproximately 5 mm³. The penetration depth of the fuel in the combustionchamber 12 drops with a pulse duration of this kind and a fuel quantityinjected in this manner per pulse so that the fuel no longer impingesagainst the wall of the combustion chamber which lies opposite to theinjection valve 16.

The depth of penetration of the fuel in the combustion chamber 12 isreduced by the discontinuous injection of the fuel into the combustionchamber 12, that is, by the injection of fuel comprising a sequence ofindividual injection pulses. The problem that the fuel deposits on thewall of the combustion chamber lying opposite to the injection valve 16is effectively reduced.

In this way, it is ensured that the fuel, which is injected into thecombustion chamber 12, is present as completely as possible as anair/fuel mixture in the combustion chamber 12 and therefore an optimalcombustion of the injected fuel takes place. This reduces the fuelconsumption and improves the emission performance, especially thehydrocarbon or soot emissions. The reduced depth of penetration of thefuel into the combustion chamber 12 has especially favorable effectswhen the wall of the combustion chamber 12 is cold, that is, for thecold start of the internal combustion engine 10. In such cases too, itcan be ensured with the method of the invention that an ignitableair/fuel mixture is present in the combustion chamber 12 of the internalcombustion engine 10.

In the diagrams shown in FIGS. 2 to 7, different embodiments of possiblepulse sequences for the fuel injection into the combustion chamber 12are shown. The individual injection pulses are identified by referencenumeral 32; whereas, the pauses between two injection pulses areidentified by reference numeral 34. The total injection of a work cycleof the internal combustion engine is identified by 36.

In the embodiment of a pulse sequence shown in FIG. 2, thetime-dependent spacings 34 between two pulses 32 are equally long overthe duration of an injection and amount approximately to 0.5 ms. Theduration of an injection pulse 32 itself is approximately 0.3 ms. In theembodiment shown in FIG. 2, the duration of the total injection 36 isapproximately 9.5 ms. For an injection quantity of 5 mm³ per injectionpulse 32, a fuel quantity of approximately 60 mm³ is injected during theinjection 36 shown in FIG. 2. For an rpm of 4,000 revolutions perminute, the time window, which is available for the injection, isapproximately 11 ms long. The fuel quantity of 60 mm³, which is to beinjected at full load, can therefore be introduced without difficultyinto the combustion chamber 12 of the internal combustion engine 10.

The embodiment shown in FIG. 3 is for an operating state of the internalcombustion engine 10 wherein the engine operates at an rpm of 5,000revolutions per minute in the part load range. This means that, for aninjection 36, a fuel quantity of approximately 30 mm³ should beinjected. The time window, which is available for an injection 36, isapproximately 9 ms long. With the six injection pulses 32 of 0.3 msduration and pauses 34 of 0.7 ms duration, a total duration of theinjection results of 5.5 seconds for an injection quantity of 30 mm³corresponding to the part load.

If, for example, a larger quantity of fuel is to be injected into thecombustion chamber 12 of the internal combustion engine 10, for example,at a higher rpm and full load, the pauses between the injection pulsescan be shortened in an embodiment (not shown). For an rpm of the engine10 of, for example, 6,000 rpm, a time window is available for theinjection of approximately 7.5 ms. In order to inject an injectionquantity of 60 mm³, 12 injection pulses are sufficient which each inject5 mm³ of fuel and which each are spaced in time from each other by 0.33ms. The total duration of the injection resulting herefrom of 7.3 mslies clearly within the time window which is available.

In the embodiment of a pulse sequence shown in FIG. 4, the duration ofthe injection pulses 32 lengthens toward the end of the total injection36. A procedure of this kind is, for example, appropriate when theinjection takes place not only during the induction phase but alsoduring the compression phase of the engine 10. Since the pressure in thecombustion chamber 12 increases during the compression phase, thepenetration depth drops with constant injection component quantity or,for the same depth of penetration, a larger injection component quantityper injection pulse 32 can be selected. In the embodiment shown, theduration of the total injection 36 is approximately 8 ms. The durationof an injection pulse 32 increases toward the end of the injection from0.3 ms to 0.5 and then further to 0.66 and finally to 0.83 ms. It isalso possible to increase the injection quantity toward the end of theinjection 36 in that the duration of the pauses 34 between two injectionpulses 32 is reduced. Such an embodiment is shown in FIG. 5.

If a stratification of a stoichiometric mixture cloud and a homogeneouslean mixture is to be generated in the combustion chamber 12 of theengine 10, then the injection strategy shown in FIG. 6 is appropriate asfollows.

An individual longer injection pulse 32 b after a longer pause 34 btakes place after a series of pulses 32 a having uniform spacings 34 a.With the starting pulse series 32 a, a homogeneous lean mixture isgenerated in the combustion chamber 12. For a piston 22 close to topdead center during the compression phase of the engine 10, so much fuelis injected into this mixture via the injection pulse 32 b that astoichiometric mixture cloud arises within the lean mixture. This modeof operation affords the advantage that also extremely lean homogeneousbasic mixtures can be combusted completely because a significant part ofthe volume was combusted stoichiometrically within the combustionchamber 12 and therefore the homogeneous lean surrounding was heated andcompressed. The advantage of the injection strategy shown in FIG. 6 isin the still further reduced fuel consumption. An injection during thecompression phase of the engine 10 further affords the advantage thatthe probability of knocking of the engine 10 is reduced.

The embodiment shown in FIG. 7 goes in the same direction wherein twoinjections 36 a and 36 b take place within a work cycle of the engine10. These injections are, in turn, comprised of individual injectionpulses 32 a and 32 b with pauses 34 a and 34 b lying therebetween.

1. A method for operating an internal combustion engine including an internal combustion engine of a motor vehicle, the method comprising the steps of: injecting gasoline from an injection valve directly into a combustion chamber of said engine with at least one injection per work cycle; injecting the gasoline of said one injection during an intake stroke as a plurality of short injection pulses spaced in time one from the other; and, causing at least one of said plurality of short injection pulses to be so short that gasoline injected into said combustion chamber does not impinge on the wall of said combustion chamber lying opposite said injection valve.
 2. The method of claim 1, wherein the gasoline quantity, which arrives in the combustion chamber with said one injection, is adjusted at least also via the duration of the individual short injection pulses.
 3. The method of claim 1, wherein the gasoline quantity, which arrives in the combustion chamber during an injection, is adjusted at least also by the number of the individual short injection pulses.
 4. The method of claim 1, wherein the injection pulses are uniformly distributed over the entire duration of an injection.
 5. The method of claim 1, wherein the duration of said short injection pulses does not change over the entire duration of said one injection.
 6. The method of claim 1, wherein the time-dependent spacing between two short injection pulses changes over the duration of said one injection.
 7. The method of claim 1, wherein the duration of one of said short injection pulses changes over the entire duration of an injection and preferably increases.
 8. The method of claim 1, wherein, at the end of an injection, an individual one of said short injection pulses takes place which takes longer than the previous short injection pulses of said one injection.
 9. The method of claim 1, wherein approximately 5 mm³ of gasoline is injected per short injection pulse and/or a short injection pulse takes no longer than approximately 0.5 ms.
 10. The method of claim 1, wherein several gasoline injections per work cycle take place of which at least one, in turn, includes several injection pulses.
 11. A computer program encoded on a computer readable medium, comprising a program suitable for carrying out a method for operating an internal combustion engine including an internal combustion engine of a motor vehicle when executed on a computer and the method including the steps of: injecting gasoline from an injection valve directly into a combustion chamber of said engine with at least one injection per work cycle; injecting the gasoline of said one injection during an intake stroke as a plurality of short injection pulses spaced in time one from the other; and, causing at least one of said plurality of short injection pulses to be so short that gasoline injected into said combustion chamber does not impinge on the wall of said combustion chamber lying opposite said injection valve.
 12. The computer program of claim 11, wherein the computer program is stored in a memory including a flash memory.
 13. A control apparatus (open loop and/or closed loop) for operating an internal combustion engine including an internal combustion engine of a motor vehicle, said control apparatus for carrying out a method for operating said internal combustion engine with said control apparatus comprising: means for injecting gasoline from an injection valve directly into a combustion chamber of said engine with at least one injection per work cycle; means for injecting the gasoline of said one injection during an intake stroke as a plurality of short injection pulses spaced in time one from the other; and, means for causing at least one of said plurality of short injection pulses to be so short that gasoline injected into said combustion chamber does not impinge on the wall of said combustion chamber lying opposite said injection valve.
 14. The control apparatus (open loop and/or closed loop) of claim 13, wherein the apparatus is provided with a computer program for carrying out said method for operating said internal combustion engine.
 15. An internal combustion engine having at least one combustion chamber and a device for injecting gasoline directly into the combustion chamber, said engine comprising a control apparatus (open loop and/or closed loop) for operating an internal combustion engine including an internal combustion engine of a motor vehicle, said control apparatus comprising means for carrying out a method for operating said internal combustion engine with said method including the steps of: injecting gasoline from an injection valve directly into a combustion chamber of said engine with at least one injection per work cycle; injecting the gasoline of said one injection during an intake stroke as a plurality of short injection pulses spaced in time one from the other; and, causing at least one of said plurality of short injection pulses to be so short that gasoline injected into said combustion chamber does not impinge on the wall of said combustion chamber lying opposite said injection valve. 